In this study, we propose to investigate in a phase II trial the therapeutic efficacy of tiazofurin in the blast crisis phase of chronic myelogenous leukemia. Blast crisis of chronic myelogenous leukemia is the terminal phase of 60-75% of patient with CML. BC is defined as the presence of 30% or more blasts in the peripheral blood or bone marrow and is often heralded by the development of extramedullary disease, bone marrow failure and other complications.